Nearcritical and supercritical water (T-c= 647 K, P-c= 22.1 MPa) is an excellent solvent for many organic compounds. Furthermore it has outstanding properties as a reaction medium because of the complete solubility of reactants, such as oxygen and hydrocarbons. To avoid the high technical demand for the supply of oxygen by compressing air, a new apparatus was developed, which produces oxygen under high pressure by means of electrolysis. For alkaline water electrolysis, an electrolysis cell was constructed working within a pressure range of 22-25 MPa and a temperature up to 623 K. Factors determining the destruction rate are, beside pressure and temperature, the electrical conductivity and the voltage used in the cell. The electrolysis cell was linked to a continuous high pressure extraction apparatus. Different aqueous waste streams (soil extracts, wool scouring wastewater, bilge water) were fed into the system and the destruction yield was studied as a function of these parameters. (C) 2000 Elsevier Science B.V. All rights reserved.